8 Answers
8

If it is possible to stop or greatly reduce the airflow between the two floors, then the problem reduces to keeping the sun from heating up the second floor. If you get some exterior (roller) window shutters for your top floor and keep them closed during the day to block the sun, that might help to keep it cooler upstairs. In the evening and night you can open the shutters and windows to let in fresh air.

Exactly this. In high summer I leave all the upstairs windows wide open in the morning while I eat my breakfast, so the cool air comes in. Then I shut them all again and put the blinds down until I come home. Often at night we sleep with all upstairs windows and doors open. This really works and costs nothing.
– RedSonjaFeb 24 '16 at 13:25

For a somewhat more long time solution, consider planting trees on the side of the house that faces the sun during the hottest part of the day. The trees will block a lot of the sunlight from hitting your house (once they are big enough).

Hot air will always rise, so either you need to stop the hot air from entering the lower floor (aka stop ventilating lower floor, which would require some other option to cool the first level), or you need to provide a way for the rising hot air to escape.

My suggestion would be to shut down/close off most of the rooms in the second floor using curtains and closed doors, but still provide a way for the hot air from below to escape. Possibly using the balcony, or one of the rooms as a vent.

If your entire second floor is closed off just like a hat, you'll only gather the heat all the time. The hotter air from below needs to escape somewhere.

I don't like the approach of opening downstairs windows and closing upstairs. I advise the opposite. This lets the hot air come upstairs (it is going there anyway), and, once it gets up there, it can escape.

The best and quickest solution I found when I was living upstairs in a non-airconditioned house:

1) open two (ONLY two) windows upstairs, ideally these are at each end of the 2nd floor.

2) place a window fan blowing OUT of one of the windows. secure the fan, and close any gaps so air doesn't blow out through the fan and sneak back in around the side of the fan.

3) close all other windows.

4) pull down blinds or curtains on all the closed windows.

.. this will produce a steady stream of air moving through the upstairs. You will notice a huge difference in a short amount of time.

In case the cause of heating of top floor is a sun:
If you have access to the roof, try to cover the roof with sunny-reflective material - foil, white tarpaulin. If your roof kind is a horizontal area with margins, you may strew a thin layer of white sand. Also you may stick some kind of heat insulation direct to ceiling.

Opening windows on the upper floor as well as the lower is the best way to get airflow in to that space. You want to encourage air to come in through the open windows on the bottom floor, and go upstairs and out the windows on the top floor.

If you have more control and flexibility over the property, you could consider installing a cool roof to reduce summer solar heating loads, plant shade trees, and/or (as a much more energy-intensive solution) install air conditioning plus insulation.